This invention relates to apparatus for automatic parenteral infusion of a liquid. More particularly, the invention relates to infusion apparatus in which the liquid to be infused into a patient is supplied at a relatively constant pressure to provide a constant, predetermined rate of infusion.
In the medical field, there is frequent need to introduce various liquids into the patient's body. Two techniques are commonly practiced but each suffer drawbacks under varying circumstances.
First, the liquid may be loaded into a conventional syringe and administered to the patient as a single injection through a hypodermic needle. As one example, diabetics may be supplied insulin using this technique. Medical science has determined, however, that it is frequently beneficial in health care to administer various medicinal liquids not at one time in a single dose, but at a slow rate over a prolonged period of time.
Such recognition gave rise to the second widely practiced technique for introducing liquids to a patient. Liquids such as saline solutions, plasma, whole blood and the like may be administered to a patient by inserting a needle into the patient's body and hanging a bottle or bag of the solution above the level of the patient so that the liquid is infused into the patient under positive pressure via flexible tubing connecting the bottle or bag and the needle. These parenteral liquid containers are typically elevated two to three feet above the patient and may be supported from a pole fastened to the patient's bed. This technique suffers from the obvious disadvantage that the patient's mobility is limited.
Oftentimes in the emergency treatment of trauma patients, intravenous solutions, for example, must be administered at the accident scene or while the patient is in route to medical facilities. Under these circumstances, the requirement of having an elevated intravenous container above the patient often presents difficulties because there is no provision for hanging the container. Thus, medical personnel must accompany the patient in order to hold the intravenous container at an appropriate, elevated position. In ambulances, helicopters, and similar medical evacuation vehicles, it may be difficult to properly position the intravenous bottle. Variations in height of the intravenous bottle above the patient will affect the pressure head of liquid and thus vary the flow rate of the solution to the patient.
To overcome the requirement of having to elevate an intravenous (IV) bottle, various apparatus have been proposed in which a flexible IV bag is pressurized either by gas pressure or by mechanical force. However, as the IV solution drains from the IV bag, the pressure force exerted on the bag also decreases thus lowering the pressure on the IV solution. This is the same problem encountered in varying the height of the bottle above the patient. To overcome this changing pressure problem, some of the known pressurized IV apparatus have a squeeze bulb which must be manually operated to increase the pressure on the IV bag as the IV solution empties therefrom. In other known pressurized IV apparatus, compressed gas from a source of compressed gas is regulated by means of a pressure regulator to maintain contant pressure on the IV bag. However, the requirement of a compressed gas source and a regulator appreciably increases the cost and complexity of the IV apparatus and, thence, the possibility of malfunction is increased.
The foregoing teachings of the prior art are embraced in the following patents.
U.S. Pat. No. 2,842,123 of Rundhaug, issued July 8, 1958 and entitled "Pressurized Tranfusion Apparatus", discloses a pressurized tranfusion apparatus having a sealed pressure container connected to a compressed gas source and having a collapsible tranfusion bag within the pressure container whereby the gas pressure acts directly on the bag to pressurize the liquid therein and to force delivery to the patient.
U.S. Pat. No. 3,153,414 by Beall et al, issued Oct. 20, 1964 and entitled "Apparatus for the Induced Infusion of Liquid from a Flexible Liquid Container", discloses infusion equipment in which an inflatable bladder encircles an intravenous liquid bag. The bladder is inflatable by a manually operated inflation squeeze bulb and exerts pressure on the intravenous bag to force fluid to the patient.
U.S. Pat. No. 3,468,308 of Bierman, issued Sept. 23, 1969 and entitled "Pressure Infusion Device for Ambulatory Patients with Pressure Control Means", teaches a collapsible bag contained within a rigid pressure shell equipped with a pressure regulating device to insure constant pressure and thus control delivery rate of intravenous liquid.
U.S. Pat. No. 3,507,278 of Werding, issued April 21, 1970 and entitled "Apparatus for Dispensing Parenteral Fluid", teaches transfusion apparatus in which a bag of liquid to be administered is contained within a rigid sealed vessel and is pressurized by gas pressure within the sealed vessel from a remote compressed gas source.
U.S. Pat. No. 3,838,794 by Cogley et al, issued Oct. 1, 1974 and entitled "Package for Storing and Dispensing Liquids", teaches a collapsible IV bag contained within a pressurized bladder connected to a regulated source of compressed air.
The teachings of the prior art, as exemplified by the foregoing references, have not been widely accepted in the medical field. As previously mentioned, gas regulating equipment adds to the cost and complexity of infusion apparatus of this genre. Medical personnel must be trained for the specific type of equipment being used and must be mindful of the varying techniques for regulating pressure on the IV solution. In spite of these significant drawbacks, however, an even more important problem exists in this equipment. It is, in fact, a potential health hazard. In the case of pressurized IV bags, the known prior art teaches pressurizing gas acting directly on the IV bag. In the event of a rupture of the IV bag, the pressurizing gas may enter the IV bag and ultimately be transmitted to the patient. The danger of air embolism is therefore thought to be the primary reason pressurized intravenous delivery equipment has not been widely utilized. Furthermore, a pressurizing gas desirable for its physical properties may be physiologically toxic if accidentally introduced to a patient due to equipment malfunction.